FT8 1500/3000

Charles Jessee

My CRKits D4D-20m is up and running! I’m using my G5RV antenna 150ft from my house and getting spots in NH (Northeast USA) all the way out to Texas and California - pretty good on what must be 10s of milliWatts emitted.

I see strong constant signals at exactly 1500 and 3000 on FT8 RX. What might those be and can I suppress them?

Thanks for an excellent kit! I’ll get that portable on my Raspberry Pi 4B soon.


Adam Rong


Congratulations on the success of building the kit. The strong signal you see on the spectrum is called Intermodulation Distortion (IMD). It is mainly caused by over driving the mixer stage. For the simplicity, let's stay with it but you can improve it by changing C5 from 104 to 105.


Charles Jessee

Hi Adam,

I did the C5 105 addition in my build. Fortunately the IMD isn't too strong and WSJT-X can decode within 100 of the signals.I got my st QSO at 1235km on CQafter dark here - I'll spread the work about the nice kits and support.